Electrical apparatus



June 28, 1966 H. F. CLARK 3,258,647

ELECTRICAL APPARATUS Filed June 6, 1962 INVENTOR. Harry E C/ar/r His Attorney United States Patent 3,258,647 ELECTRICAL APPARATUS Harry F. Clark, Dayton, Ohio, assignor to General Motors Corporation, Detroit, Mich, a corporation of Delaware Filed June '6, 1962., Ser. No. 200,576 6 Claims. '(Cl. 317-40) This invention pertains to electrical apparatus and more particularly to protecting electric motor circuits especially those having spring mounted motors and sealed casings.

Competitors efiorts to obtain maximum power from electric motors to enable them to sustain greater loads requires a quick trip overload protector set at the maximum safe value. Such quick tripping relays inherently tend to have a quick resetting time. However, a delay in the resetting time long enough to prevent a rise in temperature beyond the maximum safe value in the windings after one or more resettings is also required for protecting the motor windings under prolonged overload conditions. This is especially important in internally spring mounted electric motors within sealed casings which have a low rate of heat dissipation from the windings.

It is an object of this invention to provide a simple, inexpensive, low-cost, reliable, current-responsive, overload protector for electric motor circuits which trips open quickly beyond any maximum safe overload and which will delay resetting and reclosing long enough to prevent a rise in the motor temperature to unsafe temperatures regardless of the prolongation of the overload.

It is another object of this invention to provide a simple, inexpensive, low-cost, reliable, current-responsive, overload protector for electric motor circuits in which the tripping and resetting are independent and compensated for ambient temperature and also have different and improved characteristics as compared to protectors wherein the tripping and resetting are dependent upon the same organization.

It is another object of this invention to provide a simple,

inexpensive, low-cost, reliable, current-responsive, overload protector for electric motor circuits in which the tripping of a quick tripping current-responsive device opens the motor circuit and simultaneously starts the operation of a timer control which also opens the motor circuit and keeps it open for a sufficiently long period following the resetting of the quick tripping device.

These and other objects are obtained in the currentresponsive, overload protector illustrated in the drawings in which a first self-heated bimetal normally holds the first set of protector contacts in the closed position and is ambient temperature compensated through a second bimetal which controls the angularity of the toggle spring providing snap action of these contacts. Connected in series with the first self-heated bimetal is the operating coil of the starting relay as well as a second set of protector contacts normally held in closed position by a second self-heated bimetal which tends to close more tightly in response to increasing temperature. An actuating bimetal when heated engages and moves the second self-heated bimetal and the second set of protector contacts to the open position. Afirst heater is provided for heating the actuating bimetal and it is connected in shunt with the first protector contacts so that'it is energized to heat the actuating bimetal whenever the first protector contacts are opened. This first heater is de-energized on the opening of the second set of protector contacts. Its cooling rate determines the reset time of the second set of contacts and therefore the reset time of the protector organization.

3,258,647 Patented June 28, 1966 A second heater may be thermally associated also with the actuating bimetal to provide still longer reset times. This second heater is connected in shunt with both sets of contacts and is energized when either of the contacts are in the open circuit position. The heating rate of this sec- 0nd heater may be varied in accordance with the desired length of prolongation of the reset time. Without the second heater the organization is fully compensated for voltage variations. With the exception of the second heater, the organization is compensated for variations in ambient temperature. As soon as the first protector contacts are opened by an overload, the first heater is energized to heat the actuating bimetal to engage and move the second self-heated bimetal to open circuit position to disengage the protector contacts. The actuating bimetal together with the cooling of the second self-heated bimetal keeps the second set of contacts open for several minutes. This period may be increased readily to ten minutes by the use of the second heater. At the end of the slow cooling period of the actuating bimetal, the second set of contacts reach the closed position and the flow of current through the second self-heated bimetal quickly moves the contacts tightly together in closed position to restore the circuit for the motor.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawing wherein a preferred embodiment of the present invention is clearly shown.

In the drawings:

FIGURE 1 is a front view of the time delay device; and

FIGURE 2 is a wiring diagram showing both the tripping and resetting controls together with an electric motor circuit.

Referring now to the drawing and moreparticularly to FIGURE 2, there is shown an electric motor circuit including supply conductors 20 and 22 which supply an electric motor 24 having a main winding 26 and a phase Winding 28. The controls for the motor 24 include as a first entity the combined starting control and overload trip control 30 and as a second separate entity the reset control 32.

The supply conductor 20 connects through the conductor 34 to a normally stationary contact 36 which is normally engaged by the movable contact 38 mounted on the end on the underside of the cantilever bimetal strip 40 which is self-heated by the current flowing through it from the contacts 36, 38 through it to the conductor 42 connected to its anchored end. Connected to the conductor 42 is a solenoid'44 of the starting relay which, when energized during the initial surge of current through the main Winding 26, attracts its armature to close the phase winding contact 46 which connects the conductor 42 through the conductor 48 with the phase winding 28. The solenoid 44 connects through the conductor 50 with the normallystationary contact 52 of the reset control 32. The normally stationary contact 52 is normally engaged by the contact 54 on the underface of the end of the second self-heated cantilever bimetal strip '56 having a second end 58 anchored by the rivet 60 to the base 62 of the reset control 32. The anchored end of the bimetal 56 is connected by the conductor 64 to the adjacent end of the main winding 26. The common terminals of the main winding 26 and the phase winding 28 are connected directly to the second supply conductor 22.

The contacts 36 and 38 are normally held in closed position by a snap-acting toggle spring 66 which has its angularity adjusted for temperature by a compensating bimetal cantilever strip 68 which bends upwardly when heated and is anchored at its opposite end. Since an increase in temperature tends to bend the bimetal 40 upwardly, the temperature efi'ect upon the bimetal 68 will likewise cause it to bend upwardly and to increase the angularity of the toggle spring 66 and increase the resultant force tending to hold the contacts 36 and 38 in the closed position so that the minimum current required to open the contacts does not change with variations in ambient temperature.

Should there be an overload or current flow through the electric motor 24 beyond a maximum safe value, the bimetal 44) will snap upwardly to separate the contacts 38 and 36. This will energize the shunt circuit which includes a conductor 76 connecting with one terminal of the current responsive heater 72 having its second terminal connecting through the conductor 74 to the conductor 50 thereby shunting the contacts 36 and 38. The heater 72 is thermally associated with the L-shaped cantilever bimetal '76 which curls downwardly when heated in response to the current flow through the heater 72. This downwardly extending portion 78 is normally lightly in engagement with the second self-heated bimetal 56 adjacent the contact 54. When the bimetal 76 is heated by the heater 72, it will bend downwardly thereby bending the bimetal 56 downwardly and separating the contacts 52 and 54. The separation of the contacts 52 and 54 deenergizes the heater 72.

Because of the quick tripping characteristics of the bimetal 40, it will reclose within a relatively short time such as one minute, for example. The motor 24, however, is prevented from restarting by the previous opening of the contacts 52 and 54 by hte bimetal 76 as heated by the heater 72. The reclosing time of the contacts 52 and 54 will depend upon the time it takes the bimetal 76 to cool sufiiciently to return to its original condition to allow the bimetal 56 to move the contacts 52 and 54 to the closed circuit position. This can be arranged to be as long as three minutes.

If a circuit with a simple shunt arrangement with a single heater 72 shunting the contacts 36 and 38 does not provide a long enough off time or open circuit time of the contacts 52 and 54, a second heater 80 may be added having one terminal connected by the conductor 82 to the conductor 70 and its second terminal connected by the conductor 84 to the anchored end of the bimetal 56. This places the heater 80 in shunt with both of the protector contacts 36 and 38 and 52 and 54 so that if either is in the open circuit position, the heater 80 will be energized. The heat output of the heater 80 should be limited or the contacts 52 and 54 will never reset. The heater 80, however, may provide sufiicient heat to slow the resetting movement of the bimetal 76 so that the resetting time may be prolonged to as long as ten minutes. This long resetting time allows the motor 24 sufiicient time to recool and to prevent any objectionable rise in its temperature above the maximum safe value regardless of the motor construction or the type of motor or the enclosure provided.

The reset control 32 may be provided with a suitable enclosure 86 of an electrical insulating plastic having an anchoring boss 89 for the bimetal 76. It also provides a suitable support for the contact 52 as well as for the terminals 88 and 90 which connect to the adjacent ends of th heaters 72 and 80 to form the junction connecting with the conductor 70.

By providing independent controls consecutively operable for tripping and resetting, my overload protection system provides quick tripping for protecting the motor circuit against stall conditions and sufiiciently delayed resetting to protect against repeated attempts to restart.

While the embodiment of the present invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. A protector for an electric circuit including a firsgt set of protector contacts, first current responsive means for opening said first set of contacts, a second set of protector contacts connected in series with the first set of contacts, second current responsive means responsive to the current flowing through said second set for biasing said second set of contacts to closed position, and third current responsive means connected in shunt circuit with said first set of contacts for opening said second set of contacts.

2. A protector for an electric circuit including a first set of protector contacts, first current responsive means for opening said first set of contacts, a second set of protector contacts connected in series with the first set of contacts, second current responsive means responsive to the current flowing through said second set for biasing said second set of contacts to closed position, third current responsive means connected in shunt circuit with said first set of contacts for opening said second set of contacts, and fourth current responsive means connected in shunt with said second set of contacts for biasing said second set of contacts to the open position.

3. A protector for an electric circuit including a first set of protector contacts, first current responsive means for opening said first set of contacts, a second set of protector contacts connected in series with the first set of contacts, a current responsive bimetal means connected in series with said second set of contacts and operably connected to said second set for moving said second set to closed position in response to normal temperatures, a shunt heated bimetal means for operating to open position said second set of contacts, said shunt heated bimetal means comprising a bimetal device and a shunt heating arrangement thermally associated together, said shunt heating arrangement being electrically connected in shunt with said first set of contacts, said bimetal device having means effective when heated for operating to open position said second set of contacts.

4. A protector for an electric circuit including a first set of protector contacts, first current responsive means for opening said first set of contacts, a second set of protector contacts connected in series with the first set of contacts, a current responsive bimetal means connected in series with said second set of contacts and operably connected to said second set for moving said second set (to closed position in response to normal temperatures, a shunt heated bimetal means for operating to open position said second set of contacts, said shunt heated bimetal means comprising a bimetal device and a shunt heating arrangement thermally associated together, said shunt heating arrangement being electrically connected in shunt with said first set of contacts, said bimetal device having means effective when heated for operating to open position said second set of contacts, and a heater in heat transfer relation with said shunt heated bimetal means connected in shunt with said second set of contacts.

5. A protector for an electric circuit including a first set of protector contacts, first current responsive means for opening said first set of contacts, a second set of protector contacts connected in series with the first set of contacts, a set of opposed bimetal means for normally holding said second set of contacts in closed position including a first bimetal means responsive to the current flowing through said second set and biasing said second set of contacts closed more tightly in response to increasing current flow, said opposed bimetal means also including second bimetal means responsive to increasing temperature for opposing said first bimetal means to open said second set of contacts, and means including a shunt circuit shunting said first set of contacts for heating said second bimetal means.

6. A protector for an electric circuit including a first set of protector contacts, first current responsive means for opening said first set of contacts, a second set of protector contacts connected in series with the first set of contacts, a set of opposed bimetal means for normally holding said second set of contacts in closed position ineluding a first bimetal means responsive to the current flowing through said second set and biasing said second set of contacts closed more tightly in response to increasing current flow, said opposed bimetal means also including second bimetal means responsive to increasing temperature for opposing said first bimetal means to open said second set of contacts, and means including a shunt circuit shunting said first and second sets of contacts for heating said second bimetal means.

References Cited by the Examiner UNITED STATES PATENTS 9/1947 Vaughn 317-40 STEPHEN W. CAPELLI, Primary Examiner.

SAMUEL BERNSTEIN, Examiner.

J. D. TRAMMELL, Assistant Examiner. 

1. A PROTECTOR FOR AN ELECTRIC CIRCUIT INCLUDING A FIRST SET OF PROTECTOR CONTACTS, FIRST CURRENT RESPONSIVE MEANS FOR OPENING SAID FIRST SET OF CONTACTS, A SECOND SET OF PROTECTOR CONTACTS CONNECTED IN SERIES WITH THE FIRST SET OF CONTACTS, SECOND CURRENT RESPONSIVE MEANS RESPONSIVE TO THE CURRENT FLOWING THROUGH SAID SECOND SET FROM BIASING SAID SECOND SET OF CONTACTS TO CLOSED POSITION, AND THIRD CURRENT RESPONSIVE MEANS CONNECTED IN SHUNT CIRCUIT WITH SAID FIRST SET OF CONTACTS FOR OPENING SAID SECOND SET OF CONTACTS. 